Category Archives: SDR

For the White Tank peaks, I’m lazy. I can get the key and drive. This morning I went up to check on the radio site on the east ridge where I have an ADS-B receiver and a railroad data receiver setup. The Windows PC there had apparently died a while back, the ADS-B link failed at the beginning of April, so it was time to fix things.

The cool thing about the White Tank road is it goes through the old Caterpillar proving grounds, where they pitted Caterpillar bulldozers against the mountain. And the White Tank road was part of the testing arena.

Verrado’s north end currently ends at the golf course; the tower road is the wide diagonal that heads northwest into the narrows up-canyon.

While Verrado continues to inch its way up the lower portions of the road, it’s unlikely it’ll ever get up this far. This what I call “the bowl”, where Caterpillar dozers not only moved millions of tons of rock back and forth for test and fun, but also cut the 20%-grade, ~0.6 mile long ramp that climbs north out of the bowl and then descends into the White Tank park boundaries.

On this fine day, there’s plenty of people walking the ramp. It’s windy as heck out, and the temperatures are in the mid-50’s, but the sun is warm.

Hauled out the dead PC. Am rebuilding it now to put back on the hill in the next week or two.

Last time we visited the roof, the amp followed by the FM BCB notch filter was now in the die-cast enclosure, but not actually attached to anything. Now it finally has a home, at least for now, on the tripod leg. It required a visit to Artie’s Ace Hardware in Phoenix at Tatum and Thunderbird, which until about 8 hours ago was unknown to me as a purveyor of a near infinite number of different kinds of metric fastener! Only 4 miles away, it’s a treasure to know that I can get an M4x8 mm pan head screw even late in the afternoon.

The metric hardware was required to install the steel mounting ears on the die-cast enclosure; those mounting ears accept the muffler clamps that hold the whole thing to the leg of the tripod. Later on this winter I’ll bend up some 0.032 Al sheet to act as a sun shield and remount the box on the north leg with the shield to keep it cooler during the summer. I still need to do something permanent about the power for the amp, it’s currently the solar power setup I made a couple weeks ago.

Left is input, right is output. Runs on any voltage up to about 32 vdc and down to about 7 vdc. The internal dc-dc converter keeps the amp supplied with an even 5.0 volts.

With this amp in place, my stack’o-scanners is just bangin’ along. I’ve got great reception, and no FM BCB interference. And, there’s space in the enclosure for a future Arduino or Raspberry Pi, as well as the necessary network connection.

Is finally built. I bought three of these a couple years ago from kuyaya520 on eBay and they’ve languished since then, heat-shrink protected and tie-wrapped in place, like for the truck’s half-deaf GRE PSR-600 scanner.

Finally put one in my new die-cast case that I got 10 of last month, and used a 82 ohm resistor to set the operating voltage to around 10 vdc when running off 13.8 vdc. According to the eBay page about the amp, its best gain and noise figure is around 9-10 vdc.

Checked out the gain, and it’s pert darn near what the vendor says it is. Don’t have a simple way to do noise figure. Need to get myself an ENR noise diode so I can do y-factor.

This amp will likely go into the truck to replace the tie-wrapped kludge… I’m starting to get reasonably good at assembling these things.

Saw this 8 to 11 MHz band pass filter (item number: 201406314462) on eBay a few weeks ago and thought it might come in handy to help my SDR radios hear WWV and WWVB while not being overwhelmed by other signals.

Here’s what the 1 to 100 MHz band looks like using the PCR-1000 connected through the new antenna multicoupler, without the new filter. Remember, this antenna setup already has some significant attenuation below about 100 MHz since it’s using a VHF/UHF discone and the 10 to 2000 MHz LNA.

Here’s a plot using the ICOM PCR-1000 using the new BPF. Indeed, it has good performance, especially for the US$11.48 incl shipping.

Today I finally synced up with my friend Doug and collected from him quantity five Coilcraft 0805 10 uH chip inductors. Tiny things. Had little caffeine today, so by the time I’d returned home I was pretty steady.

Brought the LNA down from roof, opened lid, clamped assembly down to bench so it wouldn’t move, put a drop of 60/40 on one inductor pad, and with my TU-10b tweezer I picked up the part and set it in place, then tapped the one end with the soldering iron. It was harder than I thought; the part weighs nothing and has no surface friction with the tiny bead of molten solder, so it instantly moved on me.

After some re-approaching of the problem, I got the part securely attached. Checked continuity, everything looked good! Lid back on. Connected it to network analyzer, and everything did NOT look good. 20+ dB gain above about 200 MHz. The whole 10-200 MHz output level was badly attenuated, and there were strange artifacts in the low end of the spectrum. Removed the inductor and everything returned to normal. Posted a note to the designer over on gpio.com and am awaiting a response. 10 uH at 100 MHz is 6k ohms impedance, so it should be fine. The LNA was drawing its typical current (~ 160 mA).

Took another identical inductor and pressed it down on the pads with a plastic tuning stick, and did exactly the same thing as soon as it made contact. There’s something about that output circuit that doesn’t like the chip inductor.

To recap: I’ve taken the LNA that I purchased from iseeabluewhale on eBay and put it into a diecast aluminum box (purchased 10 of those from wonderco_buy on eBay as well). The TNC pigtails came from my friend Chris’ stash. The other bits and pieces came from the fossil beds of the garage.

Turned out to not be so tricky to get the thing mounted and connected.

Put it up on the roof behind the FM notch, and powered by 4 NiMH batteries.

First test – sweep 100 – 200 MHz and see what it looks like. Hopefully it looks just like the sweep from last night, just 20 dB higher.

No obvious instability or oscillation. All the signals I can hear, like NOAA weather, Arizona DPS, aviation AM, even the residual signals from FM broadcast, all clear and crisp. My my my. Looks like pretty good fidelity.

Now I’ve just got to get a source of stable dc power to the amp! And I like these little boxes…

Wasn’t able to spend any time on this the past week or so, but today I finally tracked down the pesky problems that I was having with my temporary installation.

I’d damaged one of the original TNC pigtails used to connect to the filter, and that created a sometimes 30 dB additional loss. Also, I finally found a marginal to no-good TNC-f to TNC-f adapter that I was using temporarily to connect the TNC-m connector on the box to the UHF-m connector on the cable that runs from the roof to the shack. I don’t like UHF connectors of any type, but the discone has a UHF-f connection and this cable was originally connected directly to the antenna. Until I finish my next phase of project (getting LNA into a die-cast box as well) I will leave it this way.

Using the ICOM PCR1000 receiver, here’s a plot of 50 to 150 MHz. Pretty serious FM broadcast band suppression!

Still a few broadcast stations making it through, but much better than before. The plot below is the one from a few weeks back when I first got the filter assembled into the box.

The following is what it looks like today.

What’s changed? Certainly the filter/coax assembly is doing a better job of rejecting the FM broadcast stuff, but what’s curious is the new noise floor rise that wasn’t apparent before. That noise floor rise corresponds to the band notch characteristics of the filter, but I don’t know why I didn’t see it before.

Also, the installation needs to be rid of the coax adapters that I’m using while the project is midway. Once I get the LNA into a cast box, then both the LNA and the filter into a bigger cast box, I’ll install N-f connectors on the outside of the big box and will no longer need the adapters.